Genetic structure, variability, and mating system in eastern white cedar (Thuja occidentalis) populations of recent origin in an agricultural landscape in southern Quebec

The genetic variability, genetic structure, and mating system of six small, isolated eastern white cedar (Thuja occidentalis L.) populations of recent origin from southwestern Quebec were analyzed using cellulose acetate gel electrophoresis of enzymes extracted from haploid megagametophytes. The analysis of 20 loci showed an average polymorphism of 54.2%, a mean of 1.6 alleles per locus, a mean of 1.15 effective alleles per locus, and observed and expected levels of heterozygosity of 0.116 and 0.129, respectively. There were no significant differences among the six populations for these five genetic parameters. Estimated FIS (Wrightʹs fixation indice) values indicated an excess of homozygotes as compared with the expected values under Hardy-Weinberg equilibrium. The average FST value indicated that 7.3% of the total variability could be attributed to differences among the populations. The multiloci estimates of outcrossing rate (tm) were 0.240 and 0.335, respectively, in each of two populations. Our estimates of the relative contribution of consanguineous matings to the total effective selfing rate averaged about 14%. Results suggest that vegetative propagation is the main factor contributing to family substructuring in these populations of recent origin and contrast with those reported for Ontario populations of T. occidentalis sampled in natural forest environments.